Hillslope hydrological modelling is considered to be of great importance for the understanding and quanti®cation of hydrological processes in hilly or mountainous landscapes. In recent years a few comprehensive hydrological models have been developed at the hillslope scale which have resulted in an advanced representation of hillslope hydrological processes (including their interactions), and in some operational applications, such as in runo and erosion studies at the ®eld scale or lateral ¯ow simulation in environmental and geotechnical engineering. An overview of the objectives of hillslope hydrological modelling is given, followed by a brief introduction of an exemplary comprehensive hillslope model, which stimulates a series of hydrological processes such as interception, evapotranspiration, in®ltration into the soil matrix and into macropores, lateral and vertical subsurface soil water ¯ow both in the matrix and preferential ¯ow paths, surface runo and channel discharge. Several examples of this model are presented and discussed in order to determine the model's capabilities and limitations. Finally, conclusions about the limitations of detailed hillslope modelling are drawn and an outlook on the future prospects of hydrological models on the hillslope scale is given.
The model presented performed reasonable calculations of Hortonian surface runo and subsequent erosion processes, given detailed information of initial soil water content and soil hydraulic conditions. The vertical and lateral soil moisture dynamics were also represented quite well. However, the given examples of model applications show that quite detailed climatic and soil data are required to obtain satisfactory results. The limitations of detailed hillslope hydrological modelling arise from dierent points: diculties in the representations of certain processes (e.g. surface crusting, unsaturated±saturated soil moisture ¯ow, macropore ¯ow), problems of small-scale variability, a general scarcity of detailed soil data, incomplete process parametrization and problems with the interdependent linkage of several hillslopes and channel±hillslope interactions.